Improve expiration message when rMsl effect is still up (wheals)

For example, if you cast rMsl then put on "Air, you would get a "less
protected" message when the spell ablates, even though you still had
perma-rMsl from the amulet.  Now the message in this case is "You feel
your spell is no longer protecting you from missiles."  Losing DMsl
on top of perma-RMsl gives the same "less protected" message as before.